Separation of fluid mixtures



J. W. DAVISN SEPARATION OF FLUID MIXTURES Filed D80. 19, 1955 April 26, 1960 INVENTOR. J.W. DAVI SON BY s @my A TTORNEYS :and returned to the column as reiiux.

2,933,901 SEPARATION or FLUID MIXTURES Joseph W. Davison, Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware nited States lilatent F This invention relates to a method of and apparatus dor removing selected constituents from normally'gaseous mixtures. l

It is known that ethylene andv other lowmolecular Weight unsaturated hydrocarbons can advantageously be removing .methane and hydrogen.l IWhile conventional fractionation systems can b e employed to" remove :methane and lighterlgases from gaseous mixtures, such fsystems present operating diiculties because of the exceedingly low temperatures which must b e employed,

:and have greater energy requirements for theseparation.v

In accordance with the present invention there is pro-- 'vided a systemfor separating low boiling gases,such as ymethane, from a normally gaseous-mixture containing lheavier constituents. In the present preferred embodi- :ment of this invention the feedstream is passed into a ffractionation column whichj is operated as areboiled :absorben A solvent, such as liquid propylene, is 'intro duced into the upper region of the column to absorb :the constituents heavier thanmethane. The overhead fgases from thev column are cooled and passed` to an :accumulaton Liquid is withdrawn from the accumulator from the accumulator, cooledand passed to aliquid- 'vapor separator. The liquid `from the separatoris re- ?turned to the column, preferably through the accumulator, :as reux. The gases from the -separator are allowed to expand so as to be cooled by the Joule-Thomson' effect. The cooled gases are passed in heat exchange relationship `with the gases initially removed from the accumulator. These cooled gases Vcan further be `passed in heat exchange relationship withY the feed to the column to yprovide initial cooling.

Accordingly,.it is an object of this invention to provide i an improved method of and apparatus for separating normally gaseous mixtures into selected constituents.

Another object is to provide a system for removing methane and lighter gases from hydrocarbon mixtures.

Other objects, advantages and features of the invention should become apparent from the following detailed description taken in conjunction with the-.accompanying 'drawing which is a schematic representation of apparatus employed to carry out the method of this'invention.

Gases are removedY i. i lce Patented Apr. 26, 1960 delivered to coil 17 at a constant pressure which is maintained by a pressure indicator-controller 19. A second refrigerant is supplied to an accumulator 21 by an inlet conduit 22. The level of liquid refrigerant in accumulator 21 is maintained by a liquid level controller 23 which adjusts the flow through conduit 22. Liquid refrigerant is supplied to coils 14, 15 and 16 from accumulator 21 through respective conduits 25, 26 and 2 7. The vaporized refrigerant is returned to accumulator 21 through conduits 25a, 26a and 27a. A portion of the liquid in the lower' region of column 10 is passed through a reboiler 30 by means of a conduit 31. A heating medium is circulated through exchanger 30 by means of a conduit 32. This medium is supplied to exchanger 30 at a rate so as to maintain a constant temperaturein column 10. This is controlledby a ternperature recorder-controller 33 which adjusts a flow recorder-controller 34 in conduit 32 in response to the temperature in the lower region of column 10.

.The kettle productfrom column 10 is removed through an, outlet conduit35 at a ratewhich is maintained by a liquid level controller 36.

Gases are removed from the upperregion of column 1 0 through a conduit 40 which communicates with an accumulator 41 through a heat exchanger 42. A liquid refrigerant is passed through exchanger 42 by means of a conduit 43. This refrigerant vaporizes in exchanger 42, to cool thegases passing through conduit 40. The ow of refrigerant through the exchanger is adjusted by a liquid level controller 44,which'measures the level .of liquid refrigerant within the exchanger. The condensed gases in accumulator 41 are...returned to the upper portion of 4column 19 as .reflux 'through a` conduit 46 having a pu1npv47 therein. The ow through conduit 46 is adjusted by a liquid level controller 48 on accumulator 41. A liquid solvent comprising a hydrocarbonY having three or four carbon atoms per molecule is supplied to Referring now to the drawing y.in detail, there isshown .a fractionation column 10 which isoperated as a reboiled .absorben -The feedstream to be separated is supplied to `column 11)' through an inlet conduit 11 which has a'heat exchanger 12 therein.l The feed mixture is introduced vinto column 10-at apredetermined rate which is mainwtained by a 'How recorder-controller 1 3. ACooling coils 14, 15, 16 and 17 are positioned to the upper region hof column 10. A rst refrigerant is circulated through -'coil'17 yby.means'of a conduit v18. The refrigerant is column 10 through a conduit50 which communicates with conduit 40'upstream from heat exchanger 42. The solvent is supplied at a predetermined rate which is maintained by a ilow recorder-controller 51. However, it' is not essential to the operation of this invention that the solventbe added to the lsystem at this point. If desired, theisolvent can be added directly to column 10.

conduit' 53 which passes Vthrough heat exchangers' 54 and and communicates with a knock-out drum 56.

Heaty exchanger 55 is cooled by a liquid refrigerant'which is circulated therethrough by a conduit 57. The'flow of refrigerant through conduit 57 is regulated by a liquid level controller 58. Liquid which accumulates in drum Vby a pressure recorder-controller in response to the pressure in drum 5 6.

`The operationyof the separating system of this invention can be explained by the following Aillustrative example.' .'The feedstream supplied to column 10 throughY conduit 11 has the following composition:

iMaterial: Moles per unit time Hydrogen 423 Methane 1,761

` Ethylene 1,351 Ethane 296 Propylene 493 Propane Gases .in vaccumulator 41 are removed through a The temperature of the feedstream ventering the `system is 18 F. The gases are cooled inpassing through exchanger 12 to a temperature of 56 F. .Column is operated at a pressure of 400 pounds per 'square inch absolute (p.s.i.a.). The temperatujrejfa't the bottom" of column 10 is 65 F. and the temperature at theftop of the column is 50 F. Propylene at a temperature of 1l2 F. is introduced into heatexchauger 30. This heating medium is removed from exchanger at a tetti#A perature of 69 F. Liquid ethylene Yat 65 F. is supplied to storage tank-` 21 and is directed therefrom through co-ils 14, 15 and 16V. Liquid ethane 'at 65"4 F. is supplied to coil I7 by conduit 18.

The gases removed from the top of column l10 expand slightly in passing through conduit so that the temperature of the gases at the junction with conduit is approximately F. A solvent is supplied through conduit Sti at a temperature of 28 The'con'iposil tion of the solventis as` follows: i'

Material: l Moles per unit time Propylene 1,219 Propane 57 The resulting mixture which en ters exchanger 42 is at a temperature of 32 F. These gases are cooled to 56 F. by means of liquid ethylene vaporizing in exchanger 42 at a temperature of 65 F. Accumulator41is maintained at a temperature of 756 F. and lat apressure of.395p.s.i.a. f'

` The gasesremovedfrom accumulator 41 arecooledto 99 F. after passage through exchangeri 4`'lv'hegafse's are further cooled to 112 F. afterpassing through exf changer 55. "Exchanger is cooledby ethylene vaporizf ing at 'atemperat'urelof' 120 Knockaout'drum S6 is maintained at 112"F.' and at a.v pressure of"`395 p.s.i.a. IThe gases removed from drum56are. permitted to expand to a pressure Y 66 F. after passing through exchanger.f54 and are further heatedto 28 F. after passing through exchanger 12. The kettle product from column 10 is essentially free of hydrogen and methane.

It has been discovered that, in general, thehigher the pressure in column 10, the less the overallplat energyl requirements for recoveryof ethylene at a. `gi`ven`low temperature. This applies up to suchv a pressure that the bottoms product is near the critical 4 temperaturey or pressure of the mixture, under which conditions the methane cannot effectively be reboiled from the bottoms product. Therefore, useful operating pressures'are in the range of about 300'to 500 p.s.i.a., the optimum being about l40() p.s.i.a. With Yreference to temperature, the lower the demethanizer absorbent temperature, the lower the overall plant energy requirements, down to an absorbent temperature of about 56 to 110 F. There is little difference in energy consumption between Ythese temperature levels. Therefore, useful operating temperatures are about 30 to 110 F. .absorbent tempera# ture, with 50 to 75 F. considered optimum. VTemperatureslower Vthan 75 F. are less desirable because an additional refrigeration compression stageis needed, additional investment is required for low temperature materials` of construction .and thickerjinsulation, and

.increased operating t diiculties are encountered." Thepresent invention thusprovidesial'novel'rnethod. of and 'apparatus Vfr.oi-removing,light gases such as meth e from a gaseous mixture. The absorptionoperation perof 80 p.s.i.a. which results in a cooling to 150 F. The cooled gases areheated to exchanger, third conduit lmeans mits operation ofthe column at considerably higher. ternperaturesand. .lowenrresures .than are Possible bciventional.,fractionation. Thegas expansionandlheat exchangestepsprc. de....S1.1.ffC1.1tly 10W temPfaUfeS t0 recover..additionalethyleng These low tempe obtained withv aminimumy `of Vexternal refrigeration.

should ,beh evident that 'the foregomg example ,merely illustrative of a present pre erred le'inbdir'r'lent'of the `through said fourth and column, a firstheat exchanger,

` nicatig with "the bot-tom ysoui'ce'.f an accumulator, a

changer, third conduit 4x. invention Aandvshould not beconsidered as a limitation .to the designated conditions of temperatures, pressures and compositions.

What is claimed is:

1. Separating apparatus comprising a fractionation column, a first lheat exchanger, first conduit means to introduce ya' feedstream into'said column through said first-heat exchanger, means to) remove a bottoms stream from .said column, an accumulator, second conduit means communicating between the top of said column and said accumulator', means to cool gas iiowing through `said second conduit means to condensea portion of same, means to return liquid from said accumulator to said column as reux, means to pass a solvent into the upper portion of said column, heat exchange means, a liquidgas separator, third conduit means to direct gas from said accumulator to said separator through said heat exchange means, a valve, conduit means to direct gases from said separatorlthrough said valve and then through said heatA exchange-meansand said first heat exchanger to cool gas passed to said separator and the feed stream passed to said column, means responsive to the pressure in said separator to control the opening of said valve to tend to maintain a predetermined pressure in said separator, and conduit means to pass liquid from said separator tosaid accumulator.

The combination in accordance with claim l where- 'said means to pass asolvent, communicates ,with'said Asecondconduit'mear-1s at a point upstreamvfrom where gas '3. Separating apparatus comprising -a fractionation lcolum n,'a first heat exchanger, first conduitmeans to in- .'troducefafeed stream into said column through said first with said second conduit means between said column and said third `heat exchanger fifth conduit means communieating between said-accuinulator and'said column to re- 'liquid'to said column as reiiux,'-fourthand fifth heat Y exchangers, aV liquid-gasseparator, sixth` conduit means to pass 'gas' lfrom I said accumulator to .saidseparator `fifth heat exchangers, means-to circulate aurefrigerant vfrom an external source through jsid `fifth heatexchanger, seventh conduit means to pass liquid'from said separator to said accumulator, a valve, eighth conduit means to pass gas from said separator through said valve and said fourth and first heat exchangers,` and means responsive to the pressure. in saidseparator tocontrol the opening of saidvvalve so that expansion of gasthrough said valve cools gas passed to said separator and the feed passed to said column.

i4. Separating apparatus comprising a fractionation first conduit means communicating withlsaid column through said first heat exchanger'to introduce a feed stream into said column, flow control means to maintain a predeterminedfiow through said `first'conduitmeans, second conduit meanscommue of -said'Y-column-.toremove a product streammmea 's-responsive tothe liquid level in saidui'column to controlvthe iiowthrough .said second `c :onduit means to tend to maintaln apredetermined liquid level'k in said 'iolumn,' means to heat the lower region of column" byniean'sf fea. refrigerant l fromf an external secondheat exchanger, means to circulate a .refrigerant kthroughY said .second` heatY exmeans communicating between the top vof said column and said accumulator throughsaid second-heat exchanger to remove gas .from.said column,

fourth conduit means communicating with said third conduit means between said column and said second heat exchange means to supply a solvent, fifth conduit means communicating between said accumulator and said column to return liquid to said column as rellux, means responsive to the liquid level in said accumulator to 'control the flo'w through said fth conduit means to tend to maintain a predetermined liquid level in said accumulator, third and fourth heat exchangers, a liquid-gas separator, sixth conduit means communicating between said accumulator and said separator through said third and fourth heat exchangers to pass gas from said accumulator to said separator, means to circulate a refrigerant from an external source through said fourth heat exchanger, seventh co'nduit means communicating between said separator and said accumulator to return liquid to said accumulator, eighth conduit means communicating between said separator and said third and first heat exchangers, a valve in said eighth conduit means between said separator and said third heat exchanger, and means responsive to the pressure in said separator to control the opening of said valve so that expansion o'f gas through said valve cools the gas passed to said separator through said third heat exchanger and the feed passed to said column through said irst heat exchanger.

References Cited in the le ofV this patent UNITED STATES PATENTS Brewster Nov. 1, 1938 Barton h Oct. 10, 1939 Eaton ..1 Oct. 14, 1941 Patterson Sept. 24, 1946 Gudenrath May 3, 1949 Deming Aug. 22, 1950 Rupp Nov. 7, 1950 Kniel Dec. 19, 1950 Patterson May 8, 1951 Bodle c June 19, 1951 Kniel Oct. 30, 1951 Etherington Jan. 1, 1952 Cost ---e Jan. 22, 1952 Ferro June 17, 1952 Patterson Sept. 16, 1952 Winn Jan. 12, 1954 Miller May 11, 1954 Williams July 26, 1955 Stiles Nov. 6, 1956 Koble Dec. 2S, 1956 UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION yPlatelet No..a 21,9339901 April 26V 1960 Joseph Wo Davison It is hereby certified that error appears in the printed specification of' the' above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column il.,L line l27 for "second" read third wg line 43,1 for ""ohird"4 read second.

Signeii and sealed Ehisy 29th day of November 1960@ i (SEAL) Attest:

KARL H AXLINE ROBERT C. WATSGN Attesting OHcer Commissioner of Patents 

